This invention relates to fine emulsions of polyorganosiloxanes wherein the average particle size of the polyorganosiloxane in the fine emulsion is less than about 0.3 micron. This invention also relates to microemulsions of polyorganosiloxanes wherein the average particle size of the polyorganosiloxane in the microemulsion is less than 0.14 micron. This invention also relates to a method of preparing such fine emulsions and microemulsions of the oil-in-water type. Such emulsions with small particle size droplets or aggregrates are generally translucent or transparent in appearance.
Generally, translucent or transparent emulsions are difficult to prepare. The oil-in-water type microemulsions are generally more difficult to make than the water-in-oil type microemulsions. Only a few, limited examples of polyorganosiloxanes as the oil phase in such translucent or transparent emulsions are known. Rosano in U.S. Pat. No. 4,146,499 (issued Mar. 27, 1979) teaches a method of preparing an oil-in-water microemulsion. Rosano prepared such a microemulsion in a four-step process involving (1) selection of a first surfactant which is just barely soluble in the oil phase; (2) dissolving the selected first surfactant in the oil to be emulsified in an amount effective to yield a milky or lactescent emulsion of the emulsified oil in an aqueous phase; (3) adding the oil with the dissolved first surfactant to the water phase with agitation; and (4) finally, providing a second surfactant in the water phase which is somewhat more soluble in water than the first surfactant to produce a substantially clear microemulsion of oil-in-water. The second surfactant may be either added to the aqueous phase prior to addition of the oil with the dissolved first surfactant or it may be used to titrate the lactescent emulsion prepared in the third step until the desired substantially clear microemulsion is obtained. When a hydrophobic oil, which is not readily dispersed in the aqueous medium, is employed in the method of Rosano it is necessary to first dissolve the hydrophobic oil in a solvent which can be dispersed in the aqueous medium. The hydrophobic oil dissolved in the solvent is then treated as the oil phase in the Rosano method. Rosano (Example 5) described the preparation of a microemulsion of a dimethylpolysiloxane, a hydrophobic oil, dissolved in trichlorotrifluoroethane using polyoxyethylene (20) sorbitan monolaurate as the first surfactant and nonylphenol polyethylene glycol ether as the second surfactant. Microemulsions containing other polyorganosiloxanes are neither described nor taught by Rosano. Nor is it taught that polyorganosiloxane microemulsions can be prepared without first dissolving the polyorganosiloxane in an solvent which can be dispersed in the aqueous medium.
Dumoulin in U.S. Pat. Nos. 3,975,294 (issued Aug. 17, 1976) and 4,052,331 (issued Oct. 4, 1977) teaches the preparation of polyorganosiloxane microemulsions using a surface active composition which comprises by weight (a) 45 to 90 percent of at least one n-alkyl monoether of a polyethylene glycol, containing 4 to 9 --CH.sub.2 CH.sub.2 O-- units, the n-alkyl radicals containing 5 to 15 carbon atoms; (b) 5 to 35 percent of a sodium dialkylsulphosuccinate, the linear or branched alkyl radicals containing 6 to 12 carbon atoms; (c) 2 to 17 percent of at least one acid selected from oleic, linoleic, linolenic, and ricinoleic acid, and (d) 1.5 to 12 percent of at least one amine selected from triethanolamine and n-hydroxyethylmorpholine. Attempts to prepare microemulsions from polyorganosiloxanes with surfactants other than the described surface active composition failed. The method of Dumoulin can produce microemulsions which contain a maximum of 15 weight percent of the polyorganosiloxane. Also, the method of Dumoulin generally requires significant amounts of the surface active composition to prepare satisfactory microemulsions. Typically the amount of surface active composition required was in the range of about 200 to 1000 parts by weight per 100 parts by weight of the polyorganosiloxane to be microemulsified.
Cekada and Weyenberg in U.S. Pat. No. 3,433,780 (issued Mar. 18, 1969) teach the preparation of colloid suspensions (particle size less than 0.1 micron) of silsesquioxanes of unit formula RSiO.sub.3/2 where R is a hydrocarbon or substituted hydrocarbon radical containing from 1 to 7 carbon atoms. These suspensions or microemulsions were prepared by adding the appropriate silane to a water-surfactant mixture, with agitation, the amount of silane being (1) less than 10 percent by weight or (2) the silane being added at a rate of less than ten moles of silane per liter per hour. The method of Cekada et al. is limited to the preparation of siloxanes of general formula RSiO.sub.3/2 only. The procedure of Cekada et al. is an example of emulsion polymerization.